The presently disclosed embodiments relate generally to a method and system for magnetic actuated mixing which use magnetic particles and a varying magnetic field to facilitate the mixing to prepare latex emulsions.
Numerous processes are within the purview of those skilled in the art for forming toners. Emulsion aggregation (EA) is one such method. EA toners are generally formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex emulsion by first forming a seed polymer. Other methods of emulsion/aggregation/coalescing for preparing toners are illustrated in U.S. Pat. Nos. 3,644,263; 3,879,327; 4,243,566; 5,403,693; 5,418,108; 5,364,729; 5,346,797; 5,527,658; 5,585,215; 5,650,255; 5,650,256; 5,501,935; 7,683,142; 7,977,024; 8,124,309; 8,163,459; and 8,168,699, the disclosures of which are hereby incorporated by reference in their entirety.
Polyester toners have been prepared utilizing amorphous and crystalline polyester resins. The incorporation of these polyester resins into toner requires that the resins first be formulated into emulsions prepared by solvent containing batch processes, for example solvent-based phase inversion emulsification (PIE). PIE is currently the main process of forming emulsified polyester resin latex for use in polyester emulsion aggregation toners. Ammonium hydroxide (NH4OH) is commonly used as a “basic neutralization agent” in the polyester emulsification process. The ammonium hydroxide inverts the resin dissolved oil phase (resin/solvent solution) in water to form a stable aqueous emulsion.
In the PIE process, the type of base or neutralizing agent and ratio of neutralizing agent to resin or solvent plays a very critical role. There are many input process parameters such as resin composition, resin molecular weight and acid value that can vary which make it difficult to emulsify high molecular weight branched amorphous polyester resins to produce the desired particle size range (e.g., 100-250 nm) and a narrow particle size distribution.
In a batch process for preparing resin latex, the mixing step is one of most critical steps to determine the overall performance of the process. For example, in applications where small-sized particles are produced, achieving the small scale and uniform distribution of the particles is determined by the mixing step. Present mixing methods and systems do not provide uniform mixing efficiency across the entire mixing zone and are only localized at the central mixing point, for example, where the impeller tip is located. As shown in FIG. 1, a typical type of mechanical impeller mixing system 5 has conventionally been used. However, as seen, such systems suffer from non-uniform mixing efficiency across the whole mixing zone and the high mixing field 10 only localized at the impeller tip 15. The mixing strength decays as the distance increases from the impeller 15. Dead spots or shallow spots with inefficient mixing 20 are distributed along the shaft edge 25. Attempts at improvement demonstrated that global uniformity could not be easily handled by the mechanical mixing. Careful selection of a mechanical system to avoid its resonance adds further complexity.
Improvements on mixing methods and systems often generate more complex setups which have their own set of problems, such as increase mechanical maintenance of parts. Recently, acoustic mixing has been used to avoid inefficient mixing. As shown in FIG. 2, an acoustic mixing system 30 uses a non-contact mean to provide micro scale mixing 35 within a micro zone of about 50 μm in a closed vessel 40. However, generating the acoustic wave still relies on mechanical resonance as controlled by engineered plates, eccentric weights and springs. Special care and protection of the mechanism to generate mechanical resonance is typically used and any small turbulence may cause catastrophic damage on the system. Therefore, the overall service life is still limited to the effective lifetime of the mechanical components. Thus, such systems, as exemplified in U.S. Pat. No. 8,124,309, are not free of mechanical maintenance. In addition, the acoustic energy also decays at distances far away from the source.
There is thus a need for a new and improved mixing method and system that overcomes the problems encountered with the conventional systems being used as described above.